The instant invention relates to electroactive polymers, particularly electroluminescent polymers, that are block polymers, and to processes for making such block polymers.
Highly conjugated polymeric materials have been taught to be useful as semiconductors. See e.g. U.S. Pat. No. 6,204,515. Burroughes et al. discovered that certain conjugated polymeric materials, specifically polyphenylene vinylene (PPV), were electroluminescent and thus could be used in light emitting diodes. Burroughes et al., xe2x80x9cLight-emitting diodes ased on conjugated polymersxe2x80x9d Nature, vol. 347, pp. 539-541, October 1990.
Extensive work has occurred since this initial discovery. This work includes use of variations of PPV as well as other types of conjugated polymersxe2x80x94e.g. polythiophenes, polyfluorenes. See e.g. Fukuda, xe2x80x9cSynthesis of Fusible and Sluble Conduscting polyfluorene Derivatives and their Characteristicsxe2x80x9d J. of Poly. Sci., vol. 31, pp. 2465-2471, 1993, and U.S. Pat. No. 5,708,130. Polymers containing more than one type of monomer unit have also been taught. See e.g. WO 00/46321. Finally, blends of conjugated polymers have been taught to be especially effective as they may allow adjustment of the overall composition to maximize various desired properties, such as emission wavelength, efficiency, lifetime, etc. Yu et al., xe2x80x9cEnhanced electroluminescnence from semiconducting polymer blendsxe2x80x9d, Syn . Met. 72 (1995) pp. 249-252; Kim et al., xe2x80x9cLED Characterization of an Alternating Copolymer and its Blendsxe2x80x9d SPIE vol. 3148, pp. 151-158; Tasch et al., xe2x80x9cEfficient red- and orange-light emitting diodes realized by excitation energy transfer from blue-light-emitting conjugated polymersxe2x80x9d Physical Review B, The American Physical Society, vol. 56, no. 8 (1997) pp. 4479-4483; and U.S. Pat. No. 6,169,163.
While some work has been done using block copolymers, these block copolymers have included blocks that are not consistently conjugated along the backbone of the polymer (because at least part of the backbone of the polymer is saturated). See e.g. Heischkel et al. xe2x80x9cSynthesis of ABC-triblock copolymers for light emitting diodesxe2x80x9d Macromol. Chem. Phys., 199, 869-880 (1998) and Chen et al., xe2x80x9cImproved efficiencies of light-emitting diodes through incorporation of charge transporting components in tri-block polymersxe2x80x9d, Syn. Met. 107 (1999) pp. 203-207 and U.S. Patent publication 2001/0024738A1.
Electroluminescent polymer devices can be made as layered systems. For example, a transparent layer of electrically conductive indium-tin oxide can be deposited on a pane of glass as the anode of the device. Then a xe2x80x9chole injectionxe2x80x9d layer of, for example, polyethylene dioxythiophene, (available under the tradename Baytron P from Bayer Corp.) can be formed on the anode. Then a layer of electroluminescent polymer can be formed on top of the hole injection layer. Then, a layer of an appropriate low work function metal, such as calcium, can be formed on top of the electroluminescent polymer layer as the cathode of the device. When an electrical potential is applied between the cathode and anode, holes or positive charge carriers are injected into the electroluminescent polymer layer from the hole injection layer while electrons or negative charge carriers are injected into the electroluminescent polymer layer from the cathode. The negative charge carriers can combine with the positive charge carriers in the electroluminescent polymer layer to generate light.
As disclosed in U.S. Pat. No. 6,204,515, herin fully incorporated by reference, semiconducting polymer field effect transistors can be prepared by forming a layer of an electrically insulating material on an electrically conducting gate layer. A layer of semiconducting polymer is formed on the layer of electrically insulating material, the layer of semiconducting polymer being in electrical contact with and between the source and drain of the transistor.
Towns et al., WO 00/55927, herein fully incorporated by reference, taught a co-polymer for use in an electroluminescent device comprised of at least two or more regions along the length of the polymer backbone. The first region is for transporting negative charge carriers. The second region is for transporting positive charge carrier. The third region is for accepting and combining the positive and negative charge carriers to generate light. While mentioning at page 4, second paragraph that the components could be combined in the main chain, side chains, in block or random copolymer form, Towns teaches only how to make random copolymers and exemplifies only random coopolymers and only polymers of two different monomers, See Example 5. Towns also indicates that the third component may be present as part of the copolymer or as a separate blended component and in Example 6 blends the random copolymer of Example 5 with another copolymer.
The various optimized polymers and polymer blends of Towns et al. are an advance in the art because they tend to optimize the energy levels and bandgap of the polymers and polymer blends. However, it would be a further advance in the art of electroluminescent polymers if the brightness, energy efficiency and lifetime of electroluminescent devices made from electroluminescent polymers could be further improved.
Applicants have found that certain specifically designed block polymers surprisingly function better in electroluminescent devices (better brightness, energy efficiency and lifetime) than: (a) random polymers of the same monomers; or (b) blends of random polymers of the same monomers.
More specifically, the instant invention is an organic block polymer useful in an electroluminescent polymer device, comprising: (a) an emissive polymer block that is consistently conjugated along the backbone of the emissive polymer block (e.g., a copolymer of 2,7-linked 9,9 dioctyl fluorene and 4,7-linked 2,1,3-benzothiadiazole); and at least one of the following: (b) a positive charge carrier polymer block that is consistently conjugated along the backbone of the positive charge carrier polymer block (e.g., a copolymer of 2,7-linked 9,9-dioctylfluorene and 4,4xe2x80x2-linked N,Nxe2x80x2-di(3-carbomethoxyphenyl)benzidine) for transporting positive charge carriers to the emissive polymer block so that the positive charge carriers can combine with negative charge carriers to generate light, (c) a negative charge carrier polymer block that is consistently conjugated along the backbone of the negative charge carrier polymer block for transporting negative charge carriers to the emissive polymer block so that the negative charge carriers can combine with positive charge carriers to generate light, and (d) a host polymer block that is consistently conjugated along the backbone of the host block for providing a matrix for emitter that affords Forster energy transfer and minimization of concentration quenching effects.
In another embodiment the instant invention is an improved electroluminescent polymer device that includes an anode, a cathode and an electroluminescent polymer positioned between the anode and the cathode, wherein the improvement comprises: the electroluminescent polymer being an organic block polymer comprising an emissive polymer block that is consistently conjugated along the backbone of the emissive polymer block and a positive charge carrier polymer block that is consistently conjugated along the backbone of the positive charge carrier polymer block.
In yet another embodiment, the instant invention is an improved semiconducting polymer field effect transistor that includes a semiconducting polymer positioned between and in electrical contact with a drain and a source, wherein the improvement comprises: the semiconducting polymer being an organic block polymer comprising an emissive polymer block that is consistently conjugated along the backbone of the emissive polymer block and a positive charge carrier polymer block that is consistently conjugated along the backbone of the positive charge carrier polymer block.
In yet another embodiment, this invention is a method of making the above copolymers by synthesizing the blocks sequentially in time or by separately synthesizing the blocks followed by combination and reaction of the blocks.